Livecache and x_server - how they communicate with each other?

[kanarycab]

Hi Livecache Experts,

We recently had an issue with starting the livecache. I found out that when the livecache was stopped, they didn't stop the x_server process. When they tried to bring up the livecache, it won't come up. They tried to perform the x_server stop, kill sdb process then start x_server again but the livecache won't come up still.

So I ended up restarting the livecache server itself then start the x_server - now everything is started cleanly. Then I was able to bring the livecache.

My analysis on this is when they tried to bring up the livecache for the first time, it didn't come up since x_server wasn't stop and started cleanly. there is a kind of miscommunication between the two. Then even when you tried stopping and starting x_server after livecache start failure, it doesn't work because its already too late to do that since livecache doesn't recognize the "sdb" user/processes anymore. It made sense to me because that is the error we encountered when trying to bring up the livecache, we get "sdb user unknown"

Only when we restarted the server itself and perform a clean start then it worked. Also have to rename the dbm.shi dbm.shm processes as mentioned in  https://scn.sap.com/thread/3262926

Questions:

1. Is it required to stop the x_server and kill sdb processes when you stop the livecache?

2. What is their dependency on each other?

3. What happens when x_server is not stopped then you try to bring up the livecache? (I want someone to elaborate what happens in the background.)

4. Why is there a need to rename the dbm.shi and dbm.shm as mentioned in this thread - https://scn.sap.com/thread/3262926?

Everything is working fine right now, I just wanted this incident to be documented with the correct information and raise awareness to prevent this type of issues to happen again.

[former_member229109 · Accepted solution]

Hello,

What is the version if the liveCache kernel?

SAP MaxDB: The SAP Database - Documentation => SAP
MaxDB 7.9 Library

Questions:

1. Is it required to stop the x_server and kill sdb processes when you stop the livecache?

- NO.

2. What is their dependency on each other?

- The SAP MaxDB X servers are the communication servers of the SAP MaxDB database system. They are required to connect to databases on remote computers. Note that the JDBC interface, and therefore Database Studio, requires an X server even for local communication.

- In SAP MaxDB: The SAP Database -     Documentation => SAP
MaxDB 7.9 Library-> Glossary -> Process

  you will see the list of the MAXDB processes with short explain and more details.

3. What happens when x_server is not stopped then you try to bring up the livecache? (I want someone to elaborate what happens in the background.)

- If the x server and sdbgloballistener in new version are not started, you will be not able to access to the database remotely.

-> see MAXDB library SAP MaxDB: The SAP Database -     Documentation => SAP
MaxDB 7.9 Library-> Concepts of the Database System -> Database Tools -> Global Listener and X Servers

-> Architecture of the Database Tools :

Architecture of the Database Tools - Concepts of the Database System - SAP Library

4. Why is there a need to rename the dbm.shi and dbm.shm as mentioned in this thread - https://scn.sap.com/thread/3262926?

-> There were the shared memory corruption issuses in the old MAXDB versions.

    Don't run those steps, the root case of the issues you have has to be checked first.

-> I don't know what was the root case in the old thread. But the case was with "sdbgloballistener" processes ...

-> Please review information in note 1694323.

Regards, Natalia Khlopina

[Former Member]

Hello,

X_Server is the communication server of the Livecache/MaxDB system. It listens at service port sql6/TCP for connection requests from SAP applications/tools to livecache database.

Answer :

1. It is not required to stop x_server at time of livecache restart. But if you are performing infrastructure/server maintenance then better stop livecache from LC10 and then x_server from OS level.

2.If x_server is not running then Livecache will not start. x_server is responsible for all connections to database from SAP and tools like DB studio.

3. I have restarted livecache multiple times for maintenance but never stopped x_server (untill it is for server maintenance).

4. It was due to hanging dbmsrv process where he had to kill all processes and clean shared memory by renaming files and later starting x_server and Livecache resolved issue.

Regards,

Ashish